Resistance in South African maize inbred lines to the major ear rot diseases and associated mycotoxin contamination

Mouton, Marili (2014-12)

Thesis (MSc)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: Maize (Zea mays L.) is one of the most important grain crops produced globally and serves as the primary source of carbohydrates and vitamins to millions of people in Africa. Whenever environmental conditions are favourable, fungal species such as Fusarium verticillioides, Fusarium graminearum sensu lato, Aspergillus flavus and Stenocarpella maydis frequently infect the ears of maize, reducing yield and grain quality. Of greater economic concern is the contamination of maize kernels with mycotoxins produced by ear rot pathogens due to its association with mycotoxicoses and immune suppression in humans and animals. Outbreaks of ear rot diseases commence in the field, but their associated toxins can be produced along the value chain. Planting resistant cultivars, as part of an integrated management strategy, could provide effective means of controlling preharvest ear rot diseases and mycotoxin accumulation in maize. Maize cultivars resistant to the major ear rot fungi and their mycotoxins are not yet available in South Africa and therefore should be developed in plant improvement programmes where durable resistance is combined with useful agronomic traits. The first step in introducing resistance into maize cultivars would be to find sources of genetic resistance. Infertility or unwanted traits may be present in wild relatives or other species of maize, and therefore locally adapted breeding material would be the most desirable source. This research aimed to identify publically available maize genotypes with durable resistance to the major ear rot pathogens and their associated mycotoxins in South Africa. In this study, a collection of inbred lines with diverse genetic backgrounds and valuable agronomic characteristics were evaluated under a range of field conditions. Some inbred lines were resistant to Fusarium ear rot (FER) and fumonisin contamination during artificially inoculated trials over two years. Furthermore, these FER-resistant inbred lines have been tested for resistance to other important maize ear rot diseases including Gibberella ear rot, Diplodia ear rot and Aspergillus ear rot in a multi-location field trial. Inbred lines with low and high levels of resistance to multiple infections were identified, but significant inbred x location interactions were observed. This suggests that potentially resistant lines will require further testing in an extra season to confirm their resistant status. If confirmed, these sources could be used to investigate the underlying mechanisms conferring resistance, or to develop molecular markers to facilitate the transfer of resistance into commercially valuable cultivars.

AFRIKAANSE OPSOMMING: Mielies (Zea mays L.) is een van die belangrikste graangewasse wat wêreldwyd geproduseer word en dien as primêre bron van koolhidrate en vitamienes vir miljoene mense in Afrika. Tydens gunstige omstandighede, word die koppe van mielies dikwels geïnfekteer deur swam spesies soos Fusarium verticillioides, Fusarium graminearum sensu lato, Aspergillus flavus en Stenocarpella maydis wat lei tot ‘n afname in opbrengs en graan kwaliteit. Kontaminasie van mieliepitte met mikotoksiene wat geproduseer word deur kopvrot patogene, is egter van groter ekonomiese belang aangesien dit verband hou met mikotoksikoses en imuun onderdrukking in mens en dier. Uitbrake van kopvrot siektes begin in die veld, maar die produksie van geassosieerde mikotoksiene kan regdeur die voedselketting geskied. Die aanplanting van weerstandbiedende kultivars, as deel van geïntegreerde siektebestuurmaatreëls, kan effektief wees in die beheer van voor-oes kopvrot siektes en mikotoksien-kontaminasie. Mielie kultivars wat weerstand bied teenoor die hoof kopvrot swamme en hul mikotoksiene is nog nie in Suid-Afrika beskikbaar nie en moet dus ontwikkel word in plant verbeteringsprogramme waar duursame weerstand met nuttige agronomiese eienskappe gekombineer word. Die eerste stap in die verbetering van weerstand in mielie kultivars sal wees om bronne van genetiese weerstand te vind. Plaaslik-aangepaste teeltmateriaal bied die mees geskikte bron, omdat daar geen komplikasies van onvrugbaarheid of ongewenste kenmerke behoort te wees wat van wilde familielede of ander spesies afkomstig mag wees nie. Mielie genotipes met stabiele weerstand teen kopvrot patogene en hul geassosieerde mikotoksiene in Suid Afrika is in hierdie studie geïdentifiseer na evaluasie van ‘n versameling inteellyne met verskillende genetiese agtergronde en waardevolle agronomiese eienskappe. Na afloop van geïnokuleerde proewe is daar gevind dat sekere inteellyne weerstandbiedend is teenoor Fusarium kopvrot (FKV) en fumonisien-kontaminasie. Die FKV-weestandbiedende inteellyne is toe vir weerstand teen ander belangrike kopvrot siektes, insluitend Gibberella kopvrot, Aspergillus kopvrot en Diplodia kopvrot, getoets. Inteellyne met lae en hoë vlakke van weerstand teen verskeie infeksies is geïdentifiseer, maar ‘n beduidende inteellyn x lokaliteit interaksies is waargeneem. Dit dui daarop dat potensiële weerstandbiedende inteellyne verder getoets moet word om hul weerstandstatus te bevestig. Hierdie lyne kan dan gebruik word om die onderliggende meganismes wat weerstand teweeg bring te ondersoek of om molekulêre merkers te ontwikkel wat die oordrag van weerstand in kommersiële kultivars vergemaklik.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/86719
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